ISO 21501-3:2019

INTERNATIONAL ISO
STANDARD 21501-3
Second edition
2019-11
Determination of particle size
distribution — Single particle light
interaction methods —
Part 3:
Light extinction liquid-borne particle
counter
Détermination de la distribution granulométrique — Méthodes
d'interaction lumineuse de particules uniques —
Partie 3: Compteur de particules en suspension dans un liquide par
extinction de la lumière
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Basic configuration . 3
6 Requirements . 3
6.1 Size setting error . 3
6.2 Counting efficiency . 4
6.3 Size resolution . 4
6.4 Maximum particle number concentration . 4
6.5 Sampling flow rate error . 4
6.6 Sampling time error . 4
6.7 Sampling volume error . 4
6.8 Calibration interval . 4
6.9 Reporting of test and calibration results . 4
7 Test and calibration procedures . 5
7.1 Size setting . 5
7.1.1 Evaluation of size setting error . 5
7.1.2 Procedure of size setting . 5
7.2 Evaluation of counting efficiency . 8
7.3 Evaluation of size resolution . 9
7.4 Estimation of coincidence loss at the maximum particle number concentration .10
7.5 Evaluation of sampling flow rate error .11
7.6 Evaluation of sampling time error .11
7.7 Evaluation of sampling volume error .11
Annex A (informative) Size resolution .12
Annex B (informative) Procedure for evaluating the uncertainties of the results of the
performance tests .13
Bibliography .18
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 21501-3:2007), which has been
technically revised. The main changes from the previous edition are as follows:
— Clause 4 for “Principle” and Clause 5 for “Basic configuration” have been added;
— “size calibration” and “verification of size setting” have been combined as “size setting error” in the
requirements (Clause 6);
— “Test report” (3.10 in the previous edition) has been changed to 6.9 on “Reporting of test and
calibration results”;
— information about uncertainties has been enriched and is now the subject of Annex B.
A list of all parts in the ISO 21501 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2019 – All rights reserved

Introduction
Monitoring particle contamination levels is required in various fields, e.g. in the electronic industry, in
the pharmaceutical industry, in the manufacturing of precision machines and in medical operations.
Particle counters are useful instruments for monitoring particle contamination in liquid. The purpose
of this document is to provide a calibration procedure and verification method for particle counters, so
as to minimize the inaccuracy in the measurement result by a counter, as well as the differences in the
results measured by different instruments.
INTERNATIONAL STANDARD ISO 21501-3:2019(E)
Determination of particle size distribution — Single
particle light interaction methods —
Part 3:
Light extinction liquid-borne particle counter
1 Scope
This document describes a calibration and verification method for a light extinction liquid-borne
particle counter (LELPC), which is used to measure the size and particle number concentration of
particles suspended in liquid. The light extinction method described in this document is based on single
particle measurements. The typical size range of particles measured by this method is between 1 µm
and 100 µm in particle size.
The method is applicable to instruments used for the evaluation of the cleanliness of pharmaceutical
products (e.g. injections, water for injections, infusions), as well as the measurement of number and
size distribution of particles in various liquids.
The following are within the scope of this document:
— size setting error;
— counting efficiency;
— size resolution;
— maximum particle number concentration;
— sampling flow rate error;
— sampling time error;
— sampling volume error;
— calibration interval;
— reporting results from test and calibration.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1
calibration particles
monodisperse spherical particles with a known mean particle size, e.g. polystyrene latex (PSL) particles,
where the certified size is traceable to the International System of Units (SI), a relative standard
uncertainty of the certified size is equal to or less than 2,5 %, a refractive index that is approximately
1,59 at the wavelength of 589 nm (sodium D line)
Note 1 to entry: For spherical particles, the particle size is equal to the diameter.
3.2
counting efficiency
ratio of the particle number concentration measured by a light extinction liquid-borne particle counter (3.3)
of a certified reference material (3.7) for particle number concentration to the certified value of the CRM
3.3
LELPC
light extinction liquid-borne particle counter
instrument that measures liquid-borne particle numbers by counting the pulses as the particles pass
through the sensing volume, as well as particle size by the attenuation of light
Note 1 to entry: The optical particle size measured by the LELPC is the light extinction equivalent particle size
and not the geometrical size.
3.4
PHA
pulse height analyser
instrument that analyses the distribution of pulse heights
3.5
size resolution
measure of the ability of an instrument to distinguish between particles of different sizes
3.6
coincidence loss
reduction of particle count caused by multiple particles passing simultaneously through the sensing
volume and/or by the finite processing time of the electronic system
3.7
CRM
certified reference material
particle suspension, typically polystyrene latex particles suspended
in pure water, sufficiently homogeneous and stable, characterized for the mean particle size and number
concentration by a metrologically valid procedure, accompanied by a reference material certificate
that provides the associated uncertainties for the traceable values, and a statement of metrological
traceability
Note 1 to entry: If no CRM standards are available, the use of a particle suspension characterised with
corresponding uncertainties for particle size and concentration is sufficient
...